While not limited thereto, the present invention is particularly adapted for use with longwall mining machines and coal plows. In the mining of coal veins by the longwall mining method, a cutting machine is employed that cuts along the longwall face of the coal seam while moving longitudinally along the longwall face on a conveyor or track spaced therefrom. A suitable cutting machine for performing this operation usually consists of a machine body movable along the conveyor, and one or more support arms pivotally attached to the body and carrying rotating cutting tools.
A longwall mining machine of this type can be advanced by means of a winch arrangement comprising a chain wheel which is in engagement with a chain looped about a guide wheel and anchored at its opposite ends to the ends of the longwall face. With this arrangement, rotation of the chain wheel by a drive motor will cause the mining machine to advance along the track on which it is mounted. In other cases, however, movement of the mining machine along the face being mined is achieved by means of a gearwheel on the mining machine which engages a rack extending along the track. Such mining machines are shown, for example, in U.S. Pat. Nos. 1,710,801 and 1,638,507.
In a rack-driven mining machine of the type described above, it is difficult to produce the forward thrust required for a mining operation. These difficulties are due mainly to the undulating, uneven mine floor which impairs meshing of the driving gearwheel with the teeth of the gear rack. This is particularly true in the case of long mining machines where the undulating condition of the floor impedes the transmission of substantial thrust forces.